This invention relates to a wheel construction, such as a wheel construction to be used for grocery carts, dollies, hand trucks and the like, and more especially to wheel constructions for such carts including a hub, a central bearing assembly, a rim, a web connecting the rim and hub, and a tread on the rim.
A variety of wheel constructions having a tread positioned on the rim of a wheel are known. Many employ polyurethane rubber treads for its superior wearing qualities, for its long life, cushioning characteristics, resistance to abrasion, and resistance to weather deterioration. However, polyurethane rubbers are relatively expensive, as compared to typical wheel construction materials, such as polypropylene, and therefore it is important to minimize the amount of polyurethane used, while maximizing the effectiveness of the polyurethane, as by properly positioning it, and by wasting a minimum of it.
Typical composite wheel constructions which utilize a wheel having a central hub, web and rim, and a tread for the rim, as well as inserted or insertable bearings arrangements include those shown in U.S. Pat. Nos. 3,387,894; 3,578,812; 3,666,322; 4,072,373; 4,095,846; 4,135,763 and 4,217,944;.
A need remains for an efficiently manufactured, easily assembled, long-lived wheel construction, especially for shopping carts which are notoriously subject to heavy use and great abuse. It is, therefore, desirable to provide wheel constructions which have a tread of a long-lived material and a wheel rim which is made of a relatively inexpensive material, and one which rolls quietly on hard surfaces, resists abuse, as when the wheel is rammed into curbs or walls, resists undue transfer of shock loads to the associated bearings, and is long-lived.
It is therefore an object of the present invention to provide a wheel construction wherein a wheel comprising an interconnected hub and rim are formed of a first material, and the tread of the wheel is formed of another material, such as of polyurethane rubber. A further object is to provide an improved wheel construction wherein the tread is molded to and interlocked with the rim, thereby to permanently integrate it with the rim.